Boron analogs of biomolecules exhibit considerable therapeutic potential in the areas of cancer treatment, bone disorder (such as osteoporosis), hyperlipidemia and inflammation. Considerable activity has been demonstrated in cell cultures and rodent models. Most of the agents tested for acute toxicity appear to be safe. Considering, however, the reproductive and endocrine toxicity of boric acid (and its borate salts), it its important to determine whether boron analogs of biomolecules exhibit similar toxicity. The Phase I studies will focus on synthetic methods development (to produce large quantities of materials for toxicity studies), development of bioassays for determining testicular and endocrine effects, and screening of compounds using the newly developed bioassays. In Phase II studies, compounds will be tested for endocrine lesions using the rapid endocrine bioassay and to determine their relative importance for drug development. This toxicity information, combined with the pharmacological activity already observed, will then enable us to continue the development of pharmacologically active boron compounds.